Now on to wall street, and if you were watching the markets today, you saw it. Just after 1:00 p.M., A massive nose dive all because of one tweet from a trusted source. The associated press. It said there was an explosion at the white house and president obama was injured. But the tweet was false. Rebecca jarvis explains how it all unfolded. Reporter: It was the tweet that sent stocks plunging. At 1:07 pm, breaking news from the associated press "two explosions in the white house and barack obama is injured. ." The news was false. A hacker's hoax. But before the a.P. Or the president's press secretary could clear things up -- I can say the president was fine. I was just with him. Reporter: There were four minutes of panic on wall street. gone in an instant. 136 billion lost before seconds later, a full recovery. But it wasn't humans driving stocks lower. Traders say many computer programs troll the internet for key rases and react accordingly. In this case, they saw the ap's tweet and responded sell, sell, sell. Computers don't have emotions. Computers don't have intuition. Computers trade off of one variable and one variable only. Humans use their intuitions, we can look, we can see, we can feel and touch. We knew pretty quickly it was not a true headline. Reporter: Authorities are questioning how it could happen. The a.P. Has suspended his twitter account. But in this day and age, even an obvious hoax could cost

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